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Clay minerals as a tool to monitor the widespread paleoclimatic ‎changes at the Jurassic-Cretaceous boundary in the Tethysian ‎realm ‎
Johann Schnyder, Jean-François Deconinck

Building: Muséum d'Histoire Naturelle de Genève
Room: Amphithéâtre
Date: 2018-12-05 03:10 PM – 03:30 PM
Last modified: 2018-12-05

Abstract


Earliest views of an equable warm and mostly ice-free “Mesozoic world” have been largely challenged since the pioneering works of Hallam (1984, 1986) and Frakes (1992). This evolution was notably parallel during the ’90, to the discoveries of high latitude ice evidences at certain periods (Price, 1999) and to the increasing set of oxygen isotope data obtained on various paleontological material (brachiopods, belemnite guards, mollusk shells and fish teeth). These combined efforts led to nowadays attempts of system-scale syntheses (see for example Dera et al., 2011) which reach the quality of Cenozoic paleoclimatic syntheses (e.g., Zachos et al., 2001). The common picture of Jurassic and Cretaceous paleoclimates is now largely that of both long-terms (e.g., having a ≥Myr duration) and “short-term” temperatures changes and dry/wet oscillations, that can be documented among various basins (e.g. Price et al., 1999).

The Jurassic-Cretaceous boundary is associated with one of those large-scale and long-term paleoclimatic fluctuations (Hallam 1984, 1986; Abbink et al., 2001; Schnyder et al., 2006). Evidences of at least local high latitude ice development have also been recorded (Price, 1999).

Among the paleoclimatic proxies that can be used to reconstruct past climates, clay minerals are probably one of the best of these to evaluate wet/dry long-term paleoclimatic trends (Chamley, 1989; Velde, 1995; Dera et al., 2009). The most common clay minerals used to this respect are kaolinite-which may reflect more warmer and humid climates- and smectite, which may reflect dryer and/or seasonally humid climates.

Here, we present a synthesis of clay mineral data spanning the Jurassic-Cretaceous Boundary from various basins of the Western Tethysian area. The documented stratigraphical record extends from the Late Kimmeridgian onto part of the Berriasian. Most data show an intensification of a seasonal semi-arid paleoclimate that begins in the latest Kimmeridgian-earliest Tithonian, associated to a long-term sea-level fall leading to the development of Purbeckian facies in North-West Europe (e.g., Jacquin et al., 1998). It reverses onto a more humid climate during the Berriasian. Surprisingly, most of the Tethysian sections show that the change from a dryer to a wetter climate can be precisely dated from the topmost part of calpionellids zone B, in times of rising long-term sea-level (e.g., Jacquin et al., 1998). This rather “synchronous” climatic event recorded in the Tethysian realm is thus here tentatively associated to a warming trend leading to the melting of ice at high latitudes and an overall sea-level rise.